1. Field of the Invention
The present invention relates to an inspection apparatus and an inspection method for use in inspection routines of magnetic sensors, in particularly for use in routines of inspecting a wafer-like array of magnetic sensors in terms of their magnetic property and sensitivity via magnetic property testing under predetermined environmental conditions.
The present application claims priority on Japanese Patent Application No. 2011-175337, the content of which is incorporated herein by reference.
2. Description of the Related Art
According to conventionally-known inspection routines of magnetic properties of magnetic sensors, magnetic sensors are each placed in a magnetic field which is generated using magnetic field generating coils such as Helmholtz coils and subsequently subjected to testing to measure their output signals. Inspecting each single magnetic sensor enclosed in its package needs troublesomeness treatment and may suffer a financial loss in the assembling cost of magnetic sensors which are determined as defective ones through inspection. For this reason, it is an efficient way to collectively inspect a wafer-like array of magnetic sensors. Various technologies for inspecting a wafer-like array of magnetic sensors have been developed and disclosed in various documents such as PLT 1 and PLT 2.
PLT 1 disclosed an inspection method of a magnetic sensor chip. Herein, a test probe is brought into contact with a magnetic sensor chip, and then a magnetic field generator is moved close to the magnetic sensor chip in a preparation stage of inspection. Specifically, the distal end of a coil prober approaches a magnetic sensor so as to apply a magnetic field to the magnetic sensor, thus measuring the output signal of a magnetic sensor with a test probe. The distal end of a coil prober is able to generate a magnetic field with a single directivity. For the purpose of inspecting the output signal of a magnetic sensor exposed to an external magnetic field with multiple directivities, it is necessary to rotate the relative positioning between a coil prober and a magnetic sensor.
PLT 2 disclosed an inspection method of a magnetic sensor by use of a probe card which is brought into contact with a magnetic sensor. Specifically, a probe card including a plurality of coils is brought into contact with a wafer fabricating a magnetic sensor; electric currents are supplied to the coils of a probe card so as to apply a magnetic field to a magnetic sensor, thus detecting the output signal of a magnetic sensor with the probe card. This technology is able to change the magnitude and/or the directivity of a magnetic field applied to a magnetic sensor by changing electric currents supplied to a plurality of coils included in a probe card.
PLT 3 disclosed a weak magnetic field generator and an inspection method of a magnetic sensor, which does not necessarily relate to inspection of a magnetic sensor. Herein, an external magnetic field is applied to a geomagnetic bearing sensor with sensitivity in two directions having a rectangle angle therebetween in a single plane, and then an electric signal is supplied to a geomagnetic bearing sensor, thus analyzing the output signal of a geomagnetic sensor. Specifically, this inspection method utilizes a substrate table equipped with a socket for arranging a magnetic sensor, a magnetic field generating coil, and a magnetic field sensor, wherein the detection result of a magnetic field sensor is fed back to a magnetic field generating coil.
As described above, it is an efficient way to collectively inspect a plurality of magnetic sensors rather than each single magnetic sensor. In this case, it is necessary to employ a large coil which is able to generate a magnetic field covering a relatively large inspection area encompassing a plurality of sensors. The foregoing technologies disclosed in PLT 1 and PLT 2 utilize a probe card equipped with a coil; hence, it is difficult to enlarge the size of a coil due to its structural limitation. Additionally, they may undergo local variation of a magnetic field which is generated to cover a large inspection area. That is, the foregoing technologies of PLT 1 and PLT 2 may be degraded in their accuracy of inspection results because they simply control an electric current to determine whether or not a desired magnetic field is generated with a coil
The other technology such as PLT 3 may be an effective solution to this problem because the detection result of a magnetic field sensor is fed back to a magnetic field generating coil. However, this technology needs a single table equipped with a magnetic field sensor, a socket, and a magnetic field generating coil, wherein for the purpose of preventing interference with the socket and the coil in their positioning, the magnetic sensor is arranged in the backside of the table opposite to the socket. This arrangement may not accurately detect a magnetic field affecting a magnetic sensor installed in the socket. That is, this technology may suffer from low inspection accuracy.